The invention relates to a rotor for a reluctance machine comprising a cylindrical soft-magnetic element, wherein the soft-magnetic element has cutouts for forming magnetic flux barriers.
Rotors for synchronous reluctance machines are usually equipped with a cylindrical soft-magnetic element, which is arranged coaxially on the rotor axis. In order to form at least one pole pair or gap pair, the soft-magnetic element comprises flux-conducting and flux-blocking portions, which differ from one another by a magnetic permeability of differing degree. The portion with high magnetic conductivity is characterized as is known as the d-axis of the rotor, and the portion with comparatively lower conductivity is characterized as the q-axis of the rotor. An optimal degree of efficacy of the reluctance motor and therefore an optimal torque yield is then provided when the d-axis has the greatest possible magnetic conductivity and the q-axis has the lowest possible conductivity.
This precondition is often met by the formation of a plurality of cutouts filled with air in the soft-magnetic element along the q-axis, whereby the magnetic flux in the direction of the q-axis is inhibited and as a result the permeability decreases. The soft-magnetic element constructed in this way is then mounted on a rotor shaft and fixed axially and also tangentially.
For stability reasons one or more flux barriers is/are divided into two by radially oriented inner webs. The web arrangement increases the strength of the laminated core, which in particular optimizes the rotor stability during operation. The width of the webs is low in order to keep the influence on the permeability as low as possible.
Synchronous reluctance motors are regularly fed via a frequency converter, whereby the rotational speed can rise from 0 to operating speed and can be adjusted during operation. In particular the rotational speed for starting the motor can be increased in steps. If the synchronous reluctance motor by contrast is operated in a fixed grid, the use of a starting cage is necessary in order enable asynchronous starting. As soon as the rotational speed of the rotor approaches the synchronous rotational speed, the reluctance torque becomes predominant and the rotor runs synchronously with the rotating field.
The structure of the starting cage corresponds to the embodiments in the case of standard asynchronous machines. The cage consists of individual conductor bars, which are short-circuited at the end face. The starting cage is secured to the rotor via additional cutouts in the rotor laminated core. The structure and also the production of a rotor of this type however are comparatively complex.
The object of the present invention is to further develop a rotor for a reluctance machine in such a way that the above-mentioned disadvantages are overcome.
This object is achieved by a rotor for a reluctance machine that comprises a cylindrical soft-magnetic element, which has one or more cutouts for forming magnetic flux barriers.
In a preferred embodiment of the rotor according to the invention the soft-magnetic element is embodied as a laminated core, which, as known from the prior art, is constructed from a plurality of laminations stacked one above the other in the axial direction of the rotor and insulated from one another. This design prevents the occurrence of eddy currents in the soft-magnetic element.
In accordance with the invention all or some of the flux barriers are divided by one or more webs. The arrangement of the webs on the one hand has the purpose of providing the rotor with additional stability, in particular in the radial direction. On the other hand the rotor is divided in accordance with the invention into an inner and outer rotor region. The course of the individual webs forms a closed line, which divides the rotor in the radial direction into an inner and an outer rotor region.
The arranged flux barriers ideally do not have a trans-regional course, i.e. none of the flux barriers crosses the boundary line between inner and outer rotor region. The prohibition of the trans-regional course is based on cohesive flux barrier segments. By contrast a flux barrier divided by a web can be arranged in a trans-regional manner.
The separation of the rotor into an inner and outer region influences and optimizes the starting behavior of the rotor. When using the rotor in a reluctance machine it is possible to dispense with the use of a frequency converter, i.e. the rotor construction according to the invention allows asynchronous rotor starting when a three-phase current with constant frequency is applied.
In particular, the embodiment of the outer rotor region is used for the generation of a type of starting cage, of which the effect corresponds substantially to that of a starting cage for standard asynchronous machines. Additional provisions that were previously necessary for rotors of this type for providing the starting cage are unnecessary.
The production, manufacture and operation of the rotor according to the invention are noticeably simplified. In particular at least one conductor bar of a starting cage can be replicated by the outer rotor region. In accordance with the invention the parts of the flux barriers located in the outer rotor region form parts of the starting cage. In accordance with the invention each part of the starting cage replicated in this way is part of a flux barrier, with the exception of the short-circuit rings, which are not part of the rotor active part.
By means of the rotor lamination section according to the invention it is therefore possible to produce, with use of identical rotor laminations depending on the application, both a synchronous reluctance machine with starting cage starting at the fixed grid and also a synchronous reluctance machine without starting cage and operated by frequency converter.
In an advantageous embodiment the webs are not oriented or are only partially oriented in the radial direction. The rotor regions can be divided arbitrarily by suitable orientation of the webs.
In particular the form or the specific course of the web guidance is variable. A circular course of the web guidance is expedient, such that an annular inner and/or outer region is/are produced.
An alternative web guidance, in which a rectangular or quadrangular inner rotor region is produced, is also conceivable. The outer rotor region is formed by the external rotor faces. In addition it is possible for the inner region to approach or border the outer periphery of the rotor in portions. The inner rotor region ideally has a substantially circle-like form, which in portions, in particular in the region of the q-axis, borders the outer periphery of the rotor.
The rotor advantageously has an even number of poles, in particular two, four, six or eight poles. The arrangement of the individual flux barriers corresponds substantially to the technical teaching of US patent specification U.S. Pat. No. 5,818,140, to which reference is made expressly in this regard. The rotor of U.S. Pat. No. 5,818,140 has, similarly to the rotor of the invention, merely flux barriers as electromagnetically effective elements, which flux barriers may also be filled wholly or partially with permanent magnets. In any case such a rotor has a pure flux barrier section without any additional electromagnetically effective elements. These flux barriers each extend substantially arcuately and symmetrically with respect to the q-axis of a pole segment of the rotor. Compared to the technical teaching disclosed in U.S. Pat. No. 5,818,140, the subject matter according to the invention differs however by the web guidance according to the invention, which divides the rotor into an outer and inner rotor region.
One or more flux barriers can be filled at least in part with a paramagnetic or diamagnetic filler material. The filling of the individual flux barriers with air was previously conventional. Improved rotor properties are provided however when one or more flux barriers are filled with suitable materials that have better paramagnetic or diamagnetic properties compared with air.
Suitable materials include, for example, a metal oxide and/or aluminum and/or an aluminum alloy and/or copper and/or a copper alloy and/or plastic and/or ceramic and/or a textile and/or wood. A mixture of two or more of the specified components is also conceivable.
Both rotor regions, i.e. the flux barriers of both rotor regions, are ideally filled with appropriate filler materials. However, reference is made to the fact that this is not a necessary condition for the use of the rotor according to the invention. It is also conceivable for just the inner or just the outer region to be filled with a corresponding filler material.
The two rotor regions do not necessarily have to be filled with the same filler substance. One or more flux barriers of the outer rotor region is/are particularly preferably filled with aluminum or a filler material containing aluminum alloy. A filling of this type of the outer flux barriers has sufficient conductivity, such that the conventional conductor bars of a starting cage are replicated.
In particular, one or more flux barriers of the outer rotor region is/are filled here with an electrically conductive and magnetically non-conductive filler material, in particular with aluminum or a filler material containing aluminum alloy, and at least one flux barrier, preferably a plurality of the flux barriers, ideally all flux barriers, of the inner rotor region is/are not filled with this filler material. Here, one or more flux barriers of the inner rotor region may not be filled at all, i.e. may contain air, or may be filled with another filler material, in particular with an electrically and magnetically non-conductive filler material, such as plastic, ceramic, textiles or wood and any mixtures thereof.
In accordance with a further embodiment one or more flux barriers of the inner rotor region is/are filled wholly or partially with permanent-magnetic material. The efficacy and the power factor of the electric machine are thus improved.
The filler materials can be introduced as solid material, which is inserted into the corresponding cutouts in the rotor laminated core. Alternatively one or more flux barriers can be filled by casting methods, in particular injection molding methods.
The invention also relates to a reluctance machine, in particular a synchronous reluctance machine, having at least one rotor according to the present invention or an advantageous embodiment of the present invention. The advantages and properties of the reluctance machine according to the invention clearly correspond to those of the rotor according to the invention or those of one of the advantageous embodiments of the rotor according to the invention. For this reason a repeated description is spared.
The properties of the rotor according to the invention now mean that the reluctance machine can also be operated without frequency converter on a fixed three-phase network. The embodiment of the outer rotor region serves for the construction of a starting cage, such that the rotor can be started and set in a synchronous rotational movement without frequency converter. By way of example, one or more conductor rods is/are replicated via the outer rotor region according to the invention, wherein the outer rotor region, in combination with short-circuit rings arranged on the end face of the rotor, forms a starting cage.
The invention also relates to a method for producing a rotor according to the present invention or an advantageous embodiment of the invention. In accordance with the invention at least some of the flux barriers in the rotor core are filled at least in part with a paramagnetic and/or diamagnetic medium by casting. The rotor to be produced has an inner and outer rotor region.
Furthermore, in accordance with the invention the rotor region not to be filled is acted on by an axial force. As a result, an infiltration of the filling medium into the flux barriers of the rotor region not to be filled is prevented by the filling of the flux barriers of the rotor region to be filled. By way of example the flux barriers of the outer rotor region are to be filled with a paramagnetic or diamagnetic medium. In this case an axial force, i.e. a force in the direction of the rotor axis of rotation, is applied to the inner rotor region, such that a cast-in material cannot pass into the flux barriers of the inner rotor region.
The axial force can be applied alternately to the inner and outer rotor region in order to enable a filling of the flux barriers with different materials.
A suitable clamping tool is preferably used to apply the axial force and acts on the end faces of the cylindrical rotor design from one side or both sides. The bearing surface of the clamping tool ideally corresponds approximately or exactly to the geometric dimensioning of the rotor region not to be filled.
If different filler materials are to be introduced into the flux barriers of the inner and outer rotor region, different clamping tools are preferably available, which can each apply an axial force to the inner and then to the outer rotor region. The bearing surfaces of the clamping tools correspond ideally to the geometric dimensioning of the inner and outer rotor region.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.